The issue is caused by the concurrent use of the DirectDraw engine by NXWin
and Windows NetMeeting.
To avoid the problem, NXWin could be forced to use the GDI engine instead of
DirectDraw, by issuing the command line option -engine 1.
However, this solution implies a serious drawback, which is the inability to
use the -multiwindow option, supported only by the DirectDraw engine and
fundamental to create NX Sessions in rootless mode. Moreover the overall
performance is degraded, as the GDI engine is slower than DirectDraw.